Change the slug of the books

Hi,

First of all many thanks for this plugin! It was just the thing I need and couldn’t find.

I read the previous post on how to change the slug of default books to something else.

I read:

add_filter( ‘mbdb_book_cpt’, ‘mbdb_book_slug’);
function mbdb_book_slug( $args ) {
$args[‘rewrite’] = array( ‘slug’ => ‘libro’);
return $args;
}

But where do I put this code?

Thanks!

Joris